Component level repair of blower speed controller
 

Hi all... I have a 1998 E320 4matic that is now experiencing the all-too-well-known failure of the climate control blower speed controller. I've read numerous threads here about replacement of this component (OEM versus after market, using the controller from a W140 to keep from replacing the blower, etc.), but I haven't seen anything about whether anyone ever tried to repair the controller at the component level. Has anyone tried this?

Obviously, I would consider this because I'm cheap. Granted, it's not practical to repair some electronics, but sometimes it pays off. I did the capacitor clock repair on a W123 many years ago (before the Internet existed), so I'm not beyond trying. I will say, though, that this website would have saved me a lot of time back then, since I replaced the chip too.

Anyway, unless someone says something to discourage me from trying, I'm going to break this thing open and see what falls out.

I took a look at the unit from my '87 300E and then later from my '95 E420. They are a pretty simple unit. There is a huge power transistor mounted on a heat sink with a special dielectric grease. From other posts, the grease drys out and hardens thus negating its heat dispersal qualities.
The problem I found was there is NO part number on the power transistor. Others on this forum have searched to no avail. I would hazard a guess that the price of this would be under $50 but as you know, the replacement cost of the whole unit is pushing $300 the wrong way. Good luck.
Anziani
'93 300CE 170K (almost finished with restoration)
'95 E420 117K

If you can draw the schematic of the module (or provide a link) I can give an opinion on what PN to use. If the transistor is still good then it is possible to remove it and deduce what it is with an appropriate meter, but some skill is needed.